The thing that made Maul and bit laughable was the fact that he was seen as a thick henchman who couldn't think...

Vader was scary because he was intelligent and calcualting - Luring Luke to bespin via Leia and Han.

Maul looked stupid because despite being a very good saberist or whatever word you want, Vader looked like he talked back to Palpatine and had some control over his actions where as Maul looked like the Emporer's lapdog.

A villain has to be IMO a flawed genius or something like it. Someone who promised so much yet never quite made it, like Skywalker who had exceptional talent but could not control it...